Rothamsted Symposium on Trace Elements 10 



Points from Discussion of Paper hy Prof. Wallace 



Dr. Mulder:— 



1) Your pictures with iron deficiency in oat plants showed a 

 striation of the leaves. In Holland I have seen symptoms of 

 acidity damage which was similar to these iron deficiency symp- 

 toms. They occurred in natural soil as well as in sand-peat mix- 

 tures. 



2) Magnesium deficiency in acid Dutch soil is much increased 

 by adding potassium salts and still more by adding nitrogen as an 

 ammonium compound. Nitrates always have a beneficial effect 

 on the magnesium supply of the plant probably because of an 

 increased magnesium absorption. 



Prof. Wallace:— 



1) We also have noted symptoms resembling iron deficiency 

 in cases of soil acidity damage, especially in oats, but when we 

 have attempted to control the symptoms by spraying with iron so- 

 lutions they have also disappeared without treatment and so our 

 results have been inconclusive. 



2) High potash conditions have also accentuated magnesium 

 deficiency in our experience and we should expect ammonium 

 salts to give a similar reaction from the viewpoint of NH4 being 

 a competing base. In sand culture experiments nitrate N has 

 increased the intake of magnesium and, in both greenhouse and 

 field crops, those receiving high levels of nitrogenous manuring 

 have suffered less from magnesium deficiency than comparable 

 low nitrogen crops. 



Prof. Seekles:— 



1) Damage to plants either by a deficiency or an excess of 

 manganese at a certain pH value could be explained assuming a 

 difference of activation of definite enzymes. Normally the acti- 

 vation graph of an enzyme shows an optimum at a definite con- 

 centration of ions of trace elements. Both less and more of the 

 trace element lowers the enzyme activity. 



2) Different trace elements may exert an influence on the 



